Is this ground block OK?

Davepar · #1 08-18-2006, 02:57 PM

I made my own ground block by riveting the tabs that SteinAir sells to a piece of spare .063 sheet aluminum. Total cost $3. I was pretty happy with myself until I started to wonder if this was such a good idea. Will the brass tabs and aluminum react with each other? Should I just throw some dielectric grease on there? I ran across Amit's article which looks like a very similar approach.

Picture (kind of fuzzy):

Installed:

Dave

#2 08-18-2006, 03:09 PM

I did basiclly the same thing except I went to a hobby shop and bought a piece of 1/16 thick copper sheet approx 6" square and soldered the connectors to the sheet. Then bolted the sheet to the firewall with the engine side of the bolt going to the neg terminal on the battery.

N916K · #3 08-18-2006, 03:16 PM

I second Richards method. I used a copper bar and soldered the Steinair fastons onto it. Two years later and I have had no problem. Personally I wouldn't go with the riveted approach but I have no real reason other than I like the idea of a nice soldered joint.

Ironflight · #4 08-18-2006, 03:22 PM

That looks like nice neat work Dave, but I also think that you might potentially have a problem with dissimilar metals. Back in the 1970's, the started wiring houses in our area with aluminum wiring. this was OK as long as all of the outlets and switches were also aluminum. But when people started replacing things years later, they generally used copper replacements. A few years after that, our fire department started responding to more and more burned up outlets and switches - the dissimilar metal corrosion created high resistance joints, and heat was the result.

You might not have the problem, but I used copper sheet to make my solid bus bars.

Paul

gmcjetpilot · #5 08-18-2006, 03:44 PM

The galvanic difference is about 0.50v (anodic index) and that is a max for a "controlled environment", meaning no mosture. For harsh environment 0.15v and normal 0.25v.

I think you will be fine if you keep it dry. I like the way you think with the dielectric grease. I am thinking most of the current will go thru the edge of the hole in the tabs, thru the rivet and thru the edge of the hole in the aluminum. I wounder if you could just dip and seal the whole thing, except for course the contact area or the tab and the area where the mount bolts seat.

L.Adamson · #6 08-18-2006, 07:07 PM

Being in the air conditioning business for 35 years, I've always wondered how they can shove a bunch of copper tubes through aluminum fins, then expand the copper by swedging an over sized rod through it, for a very tight fit; and not have corrosion problems.

And then you've got plenty of moisture running around the indoor coil, as well as plenty of rain water on the outdoor coil.

But of course, we've always seperated copper water or A/C lines from galvanized ductwork, as it will indeed corrode!

I do NOT know the answer to this, but always wondered....

L.Adamson

lucky333 · #7 08-18-2006, 08:32 PM

Beautiful workmanship but 1) like the others I don't like the Al-Cu interface at all. Dissimilar metals, and I would worry about fretting and oxidation of the two materials due to vibration with all those wires hanging on. 2) if the things loosen up even a bit, you'll have many entertaining electrical issues to troubleshoot as your ground integrity fades in and out.

Riveting the tabs to a copper sheet for mechanical strength and then soldering to ensure a good electrical contact seems like it would do well. I imagine the Al rivets would be OK for that application.

John

N941WR · #8 08-30-2006, 10:20 PM

Nice work Dave!

I did about the same thing but added more tabs and put a matching but smaller block on the forward side of the firewall for grounds that will be required up there.

What has got me is the number of things that need their own grounds. Many more than I would have thought and my block is over 1/2 filled and I have a day / night VFR ship. For example, there are eight grounds just for the intercom, one for each stick's PTT, one for each mic jack, one for each audio out jack, one for the audio in jack (stereo), and one for the unit itself. Who knew?

Here are the pictures:

PS. You might want to put some plate nuts under those ribs to facilitate your wire runs. Check this out:

Davepar · #9 08-31-2006, 11:18 AM

I guess we'll be the guinea pigs on this one. I thought about getting some copper sheet from McMaster-Carr (couldn't find it at Lowes), but really don't want to re-do the whole thing. I looked for some dielectric compound to squirt in there, but only found an antioxidant at Lowes. I don't think they're the same thing. I'll keep a close eye on the block when I get flying and replace it then if needed.

I didn't put any tabs on the forward side as the only thing that needs grounds (I hope) are the P-mags. I'll just put rings terminals on those and put them under one of the bolts holding on the tab block. Or maybe one under each bolt for redundancy.

I don't think I'll run out of ground tabs. Stark wired up my harness so that all the wire shields for the audio panel (pilot/co-pilot mic/phone) all join into one. In the worst case, I might have to double up some non-essentials.

Your wiring is looking good Bill. I'm right behind you. I was hoping to run some serious copper this weekend, but I got an invite to fly down to Aurora on Saturday in an RV-7. Tough choice between that and running wires on a day when the garage will be about 80 degress.

N941WR · #10 08-31-2006, 11:39 AM

Quote:

Originally Posted by Davepar

I didn't put any tabs on the forward side as the only thing that needs grounds (I hope) are the P-mags. I'll just put rings terminals on those and put them under one of the bolts holding on the tab block. Or maybe one under each bolt for redundancy.

I don't think I'll run out of ground tabs. Stark wired up my harness so that all the wire shields for the audio panel (pilot/co-pilot mic/phone) all join into one. In the worst case, I might have to double up some non-essentials.

Your wiring is looking good Bill. I'm right behind you. I was hoping to run some serious copper this weekend, but I got an invite to fly down to Aurora on Saturday in an RV-7. Tough choice between that and running wires on a day when the garage will be about 80 degress.

Dave,

The Pmags, fuel flow, and other sensors all need grounds. Not a big deal, you can always add one, later if needed.

I need to get back and finish up the wiring. Monday I put the -9 on its gear and hung the engine so that is getting my full attention right now.

After seeing the plane late Monday Nora has been pushing me to finish it so we can start traveling. What a WOMAN!

Let's see, go flying vs. working on the plane. When I get those options I always feel guilty, regardless of which I elect to do.